PS Audio Power Plant 15........

I can’t imagine what’s going on. The P15 has brought great improvement to my system.

horses for courses.
I believe it’s safe to say that different products and methods, perhaps especially in mains conditioning, in different locations (geographically on the grid) and in the context of a system (a whole kit in a room), offer different results more then not.
So nothing about this is simply black or white. It is a more wholistic thing then that.
One can believe whatever they would like about a particular product or product line but it’s relatively meaningless without Listening, in a context, over time to become understandable. And then, that is only one context.
I’ve literally taken the same kit to a different location and room and had to dance to a completely different tune. The nature of a perfectionist hobby.
That said, i’m sorry that the PS Audio isn’t working out for you. I have had great success with other components in their earlier product line and have yet to hear the Audioquest Niagara in a system that I understand. Conversely, I have a dear friend who’s kit sound I favor, who returned a Niagara for other solutions. Go figure.

Forgive me as I may be preaching to the choir here but have you given it time to settle in as big things like that can take a fair time. I would recommend at least a couple of hundred hours. 

I agree with jim204. Give it a week of active use so it can settle down in the system. I once purchased a conditioner that sounded quite terrible in my system for the first three days, and on the fourth day, it suddenly changed and started sounding fantastic. It was a used unit, with plenty of time on it.